Screen capture is typically twice the physical size of my screen!

Hi, hi

I know this is going to sound weird.

And I am possibly in the wrong section as I am using a year old Asus monitor.

(ASUS PB287Q Display 28-inch (3840 x 2160)

In conjunction with Apple Screen capture (Shift Command 4)

(High Sierra 10.13.4)

and double checking my results with ScreenFlow (Telestream)

(Version 7.3.1)

*I have observed the behaviour outlined below on numerous software versions and have contacted both ScreenFlow and Asus. But no joy.

1) Standard Apple Screen Capture

Using the standard Apple OS X screen capture.

And setting my screen resolution to 3840 times 2160 and making a screen shot (Shift Command 4) gives a resolution of 3840 times 2160.

Setting my screen to 3360 times 1890 and making a screen shot (Shift Command 4) gives a resolution of 6720 times 3780.

Setting my screen to 3200 times 1800 and making a screen shot (Shift Command 4) gives a resolution of 6400 times 3600.

I get that these numbers that anything other than max native resolution is twice as large. But why!??!

2) Double checking with Screenflow I have the same result but for Video Capture rather than single frame screen shots!

Setting my external display to a resolution of 3840 times 2160 Screen flow records a resolution of 3840 times 2160.

Setting my external display to a resolution of 3360 times 1890 means that screen flow ends up recording 6720 times 3780.

Setting my external display to a resolution of 3200 times 1800 means that screen flow ends up recording 6400 times 3600.

This is driving me nuts. Any ideas?

Paul